Q168 · Practice questionComplex unfamiliar6 marks
QUESTION 168 (6 marks)
Two very long straight wires are perpendicular to the page, apart. The left wire carries out of the page and the right wire carries out of the page. Use . Ignore other fields.
a)[3 marks]
Determine the magnitude and direction of the net magnetic field at the midpoint.
b)[3 marks]
Determine the point between the wires at which the net magnetic field is zero, giving its distance from the left wire.
WORKED SOLUTION
6 marksPractice marking scheme
ANSWER
(a) , up the page. (b) from the left wire.
Worked solution
(a) Each midpoint distance is . Counterclockwise field lines give an upward field from the left wire and a downward field from the right. Their magnitudes are and . The net is their difference, upward.
(b) Let be measured from the left wire. gives , so . The cancellation point is closer to the weaker current.
Equivalent physically justified methods and consistent equivalent units accepted.
Displayed decimals are model answers; accept appropriate significant figures and consistent rounding from stated constants.
Part a: Determine the opposing field directions using the current directions.
Part a: Calculate the individual field magnitudes.
Part a: Subtract and give the net field direction.
Part b: Equate opposing magnetic field magnitudes.
Part b: Solve with the correct distances.
Part b: State the location measured from the left wire.
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
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